Oil shale is a natural sedimentary rock containing an abundance of residual organic material which, when processed, can be made into oil and fuel products. Typically, oil shale, such as exemplified by the Green River formation in Wyoming, Colorado and Utah, has about 15-20% organic material embedded in an inorganic mineral matrix. The organic portion is composed generally of a soluble bitumen fraction and an insoluble fraction in which kerogen constitutes the bulk of the insoluble organic material. The bitumen fraction is readily solubilized by organic solvents and can be removed for refinement by physical means. The kerogen portion is characterized by its insolubility in organic solvents and is therefore more difficult to remove. In Green River oil shale, kerogen makes up about 75% of the organic components and in most all oil shale is the major organic component.
Crude shale oil is quite different from petroleum and in some respects may be considered to be intermediate in composition between petroleum and coal tar, containing significantly higher concentrations of some hetero compounds than are found in "petroleum fractions". Other properties such as high carbon to hydrogen ratio, high percentage of hydrogen content and large amounts of nonhydrocarbon organic material prevent the common refining processes developed by the petroleum industry from being efficiently applicable to the recovery of chemicals from shale oil. The oxidation of oil shale can yield valuable hydrocarbons which can be readily converted to useful products such as diesel fuel. Attempts have been made to recover chemical products from oil shale components and their derivatives by using harsh chemical oxidizing agents such as potassium permanganate. However, large scale operations also yield vast amounts of spent by-products, such as manganese dioxide, resulting in impurities in the product and causing significant environmental problems. Other chemical oxidants are generally uneconomic. Accordingly, chemical oxidation techniques are of only limited value.
The usual method of processing oil shale comprises crushing the matrix rock and subjecting the crushed matrix to heat in a retort to distill off the kerogen by destructive pyrolysis. However, the process degrades otherwise valuable chemical components of the kerogen. When the oil shale is destructively pyrolyzed, it yields a black, waxy material from which an asphaltene fraction can be recovered, containing considerable quantities of olefinic hydrocarbons and nitrogen-, sulphur- and oxygen-containing compounds. The asphaltene fraction in crude oils and refinery bottoms is well known in the petroleum industry and is generally recognized as the transition stage from fossil fuel source to oil. Accordingly, the economic conversion of shale oil to useful products should take into account the effective conversion of asphaltene.
The present invention provides a process for the recovery of chemicals from bitumenous material which is efficient and which does not adversely affect the environment. The process involves subjecting the bituminous material to oxidative electrolysis and separating and recovering water-soluble products from the resultant residue. Specifically, an electrolytically active slurry of the bituminous material and alkaline electrolyte is placed in the anode chamber of a cell having a cathode chamber electrolytically operative therewith. A direct current potential is applied across the anode and cathode chamber at a current density of above about 15 A/m.sup.2 for a time sufficient to effect substantial oxidative electrolysis of the bituminous material, yielding a water-soluble product and a residue. The water-soluble product is separated from the residue to yield desirable chemical products.
The process applies to the electrolytic oxidation of carbonaceous bitumens in general, including coal and tar sands as well as oil shale. With respect to oil shale, the process can be applied to the hydrocarbon fraction contained in both the solvent soluble organic portion (bitumen) and the generally insoluble organic portion (kerogen) and can be applied to the asphaltene fraction derived from shale oil as well as directly to leached oil shale.